Intercell Interference Coordination (ICIC) aims at reducing the interference between cells in a cellular system. The basic principle is to, in the own cell, on a more or less dynamic basis refrain from using certain resources, on which ‘sensitive’ terminals are allocated in neighbouring cells. In principle, if the cost of the reduced resource usage in the own cell is regarded smaller than the gain from the reduced interference in the neighbour cells; a performance gain can be achieved. A good ICIC mechanism hence requires a minimum reduction in resource utilization for a large reduction of interference.
ICIC techniques comprises e.g. frequency and time reuse, power control, and coordinated beamforming. As the names indicate, these techniques control the amount of interference generated in the time/frequency, power, and spatial domains.
Measurements and signalling to support ICIC between base stations and between base stations and terminals exist. Examples include the overload indicators for Wideband Code Division Multiple Access (WCDMA) and Long Term Evolution (LTE), and the High Interference Indicator for LTE.
FIG. 1A illustrates a user equipment in a first cell, receiving downlink data from a first base station and also interference from a downlink data transmission from a second base station to a second user equipment.
The expression “downlink” is in the present context used to specify the transmission from the base station to the user equipment, while the expression “uplink” is used to denote the transmission from the user equipment to the base station.
A problem with many ICIC mechanisms is that they are not able to follow rapid variations in traffic. Even though the existence of sensitive terminals, to which interference should be limited, can be dynamically detected, with rapidly varying and bursty traffic, it is not certain that these terminals will be receiving data at all times. As a consequence, limiting interference to these terminals is often done in vain, and the desired performance improvements are not obtained to the fullest extent.
Another problem with ICIC mechanism currently in LTE is that they require timely, and/or potentially substantial amount of, signalling over X2 between eNBs. X2 is the communication interface between the base stations, or eNBs, within a telecommunication network. Hence, network planning is needed in the sense that neighbour cell relations need to be established, as well as sufficient investments in X2 capacity.
Another problem with ICIC mechanisms currently comprised in LTE is that they do not include the spatial domain which is of interest in the context of multiple antennas at the transmit and/or receive side.
Yet another problem with current mechanisms is that it is not trivial for the base stations to obtain detailed knowledge, including the spatial domain, about the channels between the (sensitive) terminals and the other interfering base stations creating the interference. In the current specifications it is possible only to obtain (long term averaged) pathloss.